Mechanical Properties of Cementitious and Non-Cementitious System After Ageing Tests for Well Abandonment Cementing Operations

Abstract

The plug and Abandonment (P&A) are the final stage of the life cycle of an oil well. This implies that the plugging material must withstand the chemicals, temperature and well pressure to ensure its long-term integrity. Portland cement is the most used material as a safety barrier in P&A operations. However, the extreme conditions of the well have challenged the mechanical properties of Portland Cement. In this context, the present work aims to identify the adequate systems as permanent plugging material and to characterize them with a qualification process based on international references and experimental validation. Hence, four systems were tested for plug cementing operation with composition variations under pre-defined ageing conditions. Class G Portland cement slurry was used as reference to allow comparison of mechanical properties (compressive strength and tensile strength) between flexible cement paste, a system containing a mixture of Class G Portland Cement with epoxy resin and finally a system with epoxy resin only. Samples containing Class G Portland Cement were cured for 14 days under well bottom conditions (3000 psi and temperature of 174 degrees Fahrenheit) and cured for 14 days at well temperature (using a thermal bath). Samples containing resin were cured for 14 days under well bottom conditions (3000 psi and temperature of 150 degrees Fahrenheit) and cured for 14 days at well temperature (using a thermal bath). Finally, the samples were aged for 60 days in a thermal bath at well temperature and exposed to the brine which is the completion fluid composition which will be above and below in contact with the well barrier in a P & A operation. The results of the compressive strength tests of the samples aged in brine showed tha in some systems tested the reduction of the modulus of elasticity occurred, however, it was also observed the increase of the modulus of elasticity in another system. The same was true of the results of tensile strength tests of aged samples, the increase of rupture loading in some systems and reduction in the other ones were observed. The mechanical tests of the samples before and after ageing were performed to define the best system to be used in a well abandonment operation aiming for long-term integrity.